1. Field of the Invention
The invention relates to a method, an arrangement, and a device for automatically changing knife units of a knife ring of a knife ring slicing device, wherein a knife changing magazine provided with resharpened knife units is moved into a defined knife changing position relative to the knife ring in which at least some of the knife receptacles in the knife changing magazine are axially aligned with at least some of the knife receptacles in the knife ring. In particular, the invention relates also to a device for comminuting material especially in the form of a knife ring slicing device, comprising a tool ring, which has uniformly distributed about its circumference tool receptacle for the comminution tools, and comprising a unit for pushing out the comminution tools, arranged on the periphery of the device, wherein the unit for pushing the comminution tools comprises several pushing elements which are axially aligned with the comminution tools to be pushed out and are advanced and retracted axially into and out of the tool receiving units of the tool ring by means of an advancing drive. The invention furthermore relates to a knife changing magazine for automatically changing the knife units of a knife ring, wherein the knife changing magazine has areas with receptacles for the knife units of a knife group to be exchanged at once.
2. Description of the Related Art
For producing wood strands as the starting material for manufacturing board-shaped structural components, slicing machines are known whose comminution tools are arranged in a stationary or rotating knife ring and operate relative to a stationary or rotating abutment. The strands produced in this way pass in the radial direction through the knife ring. The quality of the final product is greatly affected by the quality of the strands used as the starting material. The strands should have cut surfaces as smooth as possible and also identical dimensions. In order to ensure a constantly high quality of the strands, it must be ensured that the comminution tools always have sharp cutting edges in order to achieve comminution by means of cutting and, to a lesser degree, by squeezing or breaking or grinding. Sharp comminution tools have also the advantageous side effect of a reduced electric energy consumption of the comminution machine.
During operation of a comminution machine, the comminution tools are subjected to natural wear. The degree of wear depends on various factors, for example, the type of wood and moisture contents of the wood of the starting materials as well as the advancing speed and circumferential speed of the cutting tools as well as on constructive parameters such as the cutting angle and the material properties of the comminution tools. The strongest wear effect can be observed on the cutting edges of the comminution tools which become more and more blunt with increasing service life so that during the generation of wood strands a smooth cut can no longer be ensured. This causes at the same time a decrease of the strand quality, an increase of the undesirable proportion of fine particles in the wood strands and, as a result of this, an increase of the required amount of bonding agent as well as an increase of energy consumption of the slicing machine.
In order to avoid these disadvantages, it is required to perform a knife exchange in regular intervals wherein the worn or spent comminution tools are replaced by resharpened ones. Under regular conditions such a knife exchange is carried out in time intervals of three to eight hours. Since all comminution tools of a knife ring must be exchanged in such a knife exchange operation, this requires a considerable temporal expenditure which causes long downtimes of a comminution machine. In connection with known methods and devices for exchanging the comminution tools, which are performed manually or semi-automatically, a knife exchange takes approximately 20 to 40 minutes. For an average service life of the comminution tools of four hours, this causes a production loss of three hours per day. Accordingly, the resulting product loss relative to a nominal strand production output makes it necessary to design the comminution device for higher comminution output in order to ensure the continuous further processing of the produced strands in the subsequent processing steps. This entails providing larger bunker capacities as a buffer for bridging the production loss caused by the knife exchange.
In order to circumvent these disadvantages, attempts have been made to shorten the duration for a knife exchange. From German patent application 199 21 383 A1 and U.S. Pat. No. 5,313,696, a method and a device for changing the comminution tools of comminution devices are known in which the complete knife ring of the comminution device is removed and replaced by a second knife ring furnished with resharpened comminution pools.
For removing the worn or spent knife ring according to German patent application 199 21 383 A1, a tool exchange carriage is used which is moved in front of the end face of the comminution device and provides together with attachments of the comminution device a path on which the knife ring, detached from its fastening means, can be pulled axially out of the housing of the comminution device onto the carriage.
For demounting the knife ring, U.S. Pat. No. 5,313,696 suggests to arrange it, including its attachment components, its positioning components, and its drive components, on a support whose path, extending parallel to the axis of rotation, enables an axial movement of the complete comminution unit before the knife ring is removed by means of a crane and replaced by a newly furnished knife ring.
The disadvantage of these solutions is that for a knife exchange the complete knife ring must be exchanged. In addition to requiring an additional knife ring, this results in a great technical expenditure, for example, for a tool change carriage and the elements connected thereto for coupling the carriage or for a support for axially pushing out the complete comminution unit. The labor expenditure for mounting and demounting the knife ring must be added to the time required for exchanging the knives of the knife ring so that this solution is not satisfactory with respect to economic efficiency.
How the actual change of the comminution tools, i.e., their mounting in and demounting from the knife ring is carried out, is not disclosed in these prior art references.
Suggestions in this respect can be taken from German patent 41 14 840 C2 describing a method and a device for exchanging the knives of a knife ring wherein here the knife ring must first be demounted from the comminution device and must be placed into a knife changing device. In this knife changing device an automatic knife exchange takes place by means of a magazine in which the knives arranged in the knife ring, after having been released from their fastening means, are first pushed out individually and sequentially from the knife ring and are then transported on a carriage axially to the magazine where they are placed in the radial direction into the magazine.
In comparison to the prior art known at the time the invention according to 41 14 840 C2 was made, this method and this device provided a significant technological advance. However, this type of knife exchange is also possible only with the knife rings being removed from the comminution device wherein the individual knives are successively exchanged. The simultaneous exchange of several knives is not possible with this method and this device.
From German patent 33 09 517 C1 a knife exchange is known which is possible with the knife ring mounted in the comminution device. For this purpose, magazines are arranged at the end face of the knife ring which are in the form of a roll for steel strip knives or a cassette for disposable (single-use) knives, wherein the knives are moved by means of an axially acting advancing device into the knife ring. These solutions are said to enable a knife exchange even during operation of a strand-producing chopping device.
A similar approach is also known from German published patent application 19 26 777. Here a magazine having dimensions matching those of the knife ring is placed axially onto the knife ring. After detachment of the fastening means of the knives in the knife ring they are pushed out simultaneously with the action of pushing in the resharpened knives on the other side of the knife ring.
The two last mentioned methods for exchanging the spent knives of the knife ring has the disadvantage that at the front side as well as at the backside of the knife ring a high technical expenditure must be provided in order to push on one side the resharpened knives into the knife ring and to remove at the opposite side the spent knives from the knife ring.
It is an object of the present invention to provide a method and a device which enable a completely automatic knife exchange which can be performed with minimal technical expenditure within an extremely short period of time.
In accordance with the present invention, this is achieved in regard to the method in that the spent knife units, after detachment of their fastening means in the knife ring, are pushed or pulled in the axial direction out of the knife ring into an empty compartment within the knife changing magazine and, subsequently, a relative movement between the knife changing magazine and the knife ring is carried out until a knife changing position has been reached in which the knife units which have been resharpened are aligned with the knife receptacles in the knife ring and the resharpened knife units are moved from the knife changing magazine in the opposite direction into the knife ring.
In regard to the arrangement this is achieved according to the invention in that a unit for releasing and fastening the knife units in the knife ring is provided, in that a pushing unit is provided which is arranged axially opposite the end faces of the knife ring and which is suitable to transport at least one knife unit positioned in the knife exchange position axially out of the knife ring into the knife changing magazine, in that at least one unit for performing a relative movement between the knife changing magazine and the knife ring is provided, and in that an insertion unit is provided which is suitable to axially push or pull at least one knife unit out of the knife changing magazine into the knife ring.
In regard to the device for comminuting, this object is achieved in that the pushing elements are arranged on a transverse beam onto which the advancing drive acts.
In regard to the knife changing magazine, this is achieved in that the knife changing magazine has at least one more receiving area than knife groups to be exchanged
The present invention is based on the principal idea that a completely automatic exchange of the knife units of a knife ring is to be enabled without requiring any human intervention. When carrying out the method, the detection, governing, and control of the individual operating states of the method are realized by a programmable automatic sequence control.
When personnel is still to be used to some extent, the knife exchange can also be performed semi-automatically. In the semi-automatic variant, the knife units are pushed out of the knife ring only partially and are then removed by hand from the knife ring and replaced by resharpened knives. This variant of the invention is suitable in connection with the device according to the invention having the pushing elements arranged on a transverse beam onto which the advancing drive acts.
The automated knife exchange makes the operator of the comminution machines according to the invention independent of the possible shortcomings of the employed personnel; often it is these shortcomings of the personnel that cause damage to the slicing machines or lower quality of the wood strands. Moreover, the knife exchange in the past required great physical expenditure and presented a great risk of injuries as a result of the great weight and the unwieldy configuration of the knife units as well as the sharp cutting edges of the knives. The automation which can be achieved by means of the invention eliminates a source of injury for the good and the health of the operating personnel.
The reduction of the downtime of the comminution machines when employing the inventive method is of economical and thus imminent importance for the operator of comminution machines. Since the knives of comminution machines must be exchanged four times, or even more frequently, each day, the time which is saved for each knife exchange by means of the present invention over the course of time results in a significant advantage with regard to costs.
The exchange of the knife units according to the invention can be realized for the mounted as well as demounted knife ring; this provides great flexibility. The method according to the invention and the device according to the invention enable an exchange of groups of knife units wherein the number of knife units in a group comprises in the extreme situation at least one knife unit and a maximum of all knife units of a knife ring. Preferred are however knife groups which contain one fourth up to one sixteenth of all knife units of a knife ring so that with a cycle time between four and 16 a complete exchange of the knife units can be performed. In this way, an optimum of time savings and a minimum of constructive expenditure, enabling a compact design of the comminution machines, are realized.
The method and the device according to the invention require only a single knife changing magazine so that the constructive expenditure is limited to a minimum. This is enabled in that simultaneously the knife changing magazine is used as a storage container for the knife units which have been resharpened for the knife exchange and, on the other hand, for receiving the worn or spent knives from the knife ring so that the manufacturing costs relative to other devices are significantly reduced.
Since the knife exchange substantially is carried out only at the forward end face of a knife ring and substantially all components for performing the knife exchange are arranged here, this configuration also enables an extremely compact and thus space-saving design. With respect to servicing and repairs, this has the advantage of improved accessibility of the device according to the invention.
For performing a relative movement between the knife ring and the knife changing magazine after the worn knife units have been pushed out from the knife ring, a movement of the knife changing magazines is preferred according to the invention even though an adjustment of the knife ring would be possible. This preference is based on the smaller mass of the knife changing magazine which therefore enables with a reduced force expenditure a quicker realization of the relative movement. For realizing the relative movement, axial movements or pivot movements of the knife changing magazines relative to the knife ring are basically also possible. According to the invention, a horizontal or vertical displacement possibility is preferred because such a configuration requires the smallest space and, in this way, the compact configuration of the device of according to the invention can be further improved. A vertically performed relative movement provides, primarily in combination with a two-level construction of the comminution machine, the advantage that the knife exchange magazine with spent knife units during the course of relative movement can be advanced, for example, to a sharpening device arranged underneath the comminution machine.
When the exchange of the knife units is not carried out at once but in a cycled fashion, after each exchange of a knife group a further relative movement between knife changing magazine and knife ring must occur in order to move a section of the knife ring to be furnished with resharpened knife units from the knife changing magazine into the exchange position so that the old knives of the knife ring can be received. In principle, this relative movement can also be performed by the knife changing magazine. However, it is advantageous to define a fictitious knife changing position into which the knife changing magazine as well as the knife ring are moved. While for the knife changing magazine, as described, a horizontal or vertical adjustment movement is suggested, the invention prefers in this connection a rotational movement of the knife ring. In this way, a decoupling, and thus simplification, of the movement sequence is realized which also has an effect in regard to a simplified configuration of the comminution device.
A preferred embodiment of the invention provides that the knife units during the steps of being pushed out and being inserted are guided additionally. This is known primarily in connection with devices in which the knife changing magazine is arranged at an axial spacing from the end face of the knife ring. By means of an additional guiding it is ensured that the knife units reach precisely the receptacles of the knife ring or of the knife changing magazine. The guide arrangement therefore contributes significantly to improving the operational safety.
The signal for the knife exchange can be realized as a function of time but also as a function of the quality of the produced wood strands. The invention prefers however an energy-dependent control of the knife exchange because, in this way, the special wear state of the knife units is taken into consideration.
The operation of a comminution device also entails that the fine material will deposit within the knife receptacles of the knife ring. Since the boundary surfaces of the receptacles are also reference surfaces for the resharpened knife units, which are adjusted relative to the reference surfaces with regard to their geometry in order to finally reach the nominal position, dirt deposits cause a falsification of the reference surfaces so that the resharpened knife units are mounted in the knife ring in a position which deviates from the nominal position. In order to prevent this, it is suggested according to the invention to perform a cleaning of the receptacles, and thus of the reference surfaces of the knife ring, between the steps of pushing the knife units out of the knife ring and inserting the resharpened knife units into the knife ring. The cleaning action can be realized mechanically by means of a slide which frees the reference surfaces from dirt deposits, for example, during insertion of and/or pushing out the knife units. A slide is suitable, in particular, for cleaning planar surfaces. Another possibility according to the invention is provided by generating a fluid flow in the receptacles of the knife ring. For this purpose, a nozzle can be arranged at the end of a receptacle where the end face is or can be introduced together with the pushing unit into the receptacles. In this way, even locations which are difficult to access can be cleaned.
A further possibility of cleaning of the receptacle of a knife ring according to the invention is the use of a milling brush which is used alone or in combination with the aforementioned measures.
In order to ensure that the knife units which have been resharpened are actually mounted in the nominal position within the knife ring after knife exchange, according to a special embodiment of the invention it is suggested to monitor by means of a measuring device the nominal position of the knife units within the knife ring. In this connection, the radial projecting length of the cutting edges of the knife units past the inner wall of the knife ring is monitored as well as the axial insertion depth of the knife units into the knife ring. Only when the control measurements indicate a proper position of the knife units, the exchange of the knife units can be continued. In this way, damage of the comminution machine is prevented which, for example, could result by a too large radial projecting length of the cutting edge into the comminution space. Particularly when carrying out a completely automated knife exchange, the realization of control measures is of great importance because monitoring by an operator, who is capable of recognizing severe mounting errors of the knife units with ease, is no longer possible. Ensuring mounting of the knife units in the nominal position by means of an additional control measurement significantly increases at the same time the quality of the produced wood strands.
The invention will be explained in the following with embodiments illustrated in the drawings in the form of a long-cut wood slicing device with rotating knife ring. It is understood that the invention is not limited to such comminution devices; devices are also included which have comparable comminution tools which are arranged in a tool ring and axially removed from or inserted into the tool ring. Screen milling elements or grinding track elements of mills are mentioned as an example in this context.